DESCRIPTION: The PI proposes to make computer models of ecosystems of unicellular organisms. A network of processes within each cell mediates its persistence and interaction with its environment. The networks within individual cells are coupled by exchanges of chemicals through the environment, forming a global network. In some of the models mutations can modify these networks, and differential reproduction of cells occurs. The PI wants to test the hypothesis that the population of cells will coevolve toward a phase transition, or boundary, between order and chaos, on three axes: (1) the dynamic axis, for characterizing the changes of state in the cells and ecosystem on a short-term or physiological time scale; (2) a coevolutionary axis, for characterizing the strategies with which cells interact; and (3) an axis of molecular diversification, for characterizing the evolution of novel molecules in the system. (I use the term "chaos" here loosely to mean disorder -- the term the PI uses -- not in the mathematical sense.) The PI will model the ecosystem as a Boolean network in the simplest analyses.